Early environment appears to affect behavior related to fear and exploration. Male C57BL/6J mice whose mothers had been exposed to predator odor (rat feces) showed higher exploratory behavior than an unexposed group (Coutellier et al., 2008). In the present study, we subjected mice from two commonly-used laboratory strains (C57BL/6J and BALB/c) to an ecologically relevant early environmental intervention. In one condition, mouse pups were exposed to predator cues (fox odor and recorded owl calls), while in a control condition, pups were exposed only to home cage bedding. They were observed as adults (n=63) in an open-field apparatus with a shelter. Strain and sex differences were significant; BALB/c mice spent less time in the open center than C57BL/6 mice (p<.001), and female mice spent more time in the center area (p=.019). The predator-exposed group appeared to spend more time in the center (18.89s vs 9.57s), but the main effect of group was not statistically significant (p=.115). A trend was seen for a three-way interaction (Strain X Sex X Group, p=.097). These results add to the literature on developmental susceptibility to ecologically-relevant environmental manipulations.